Vehicles travel along surfaces, such as a roadway, that are often graded or at an incline. In some instances, vehicles come to rest on the inclined surface. Vehicle rollback may occur during a vehicle launch from rest on the inclined surface. More specifically, during the period between brake pedal release by the driver and propulsion of the vehicle, gravity can induce vehicle movement down the inclined surface (i.e., rollback).
Hybrid powertrains typically turn off the engine when the vehicle is stopped and restart the engine when the brakes are released. Vehicle rollback may occur between the time that the brake pressure starts to decay due to pedal release, and the time that sufficient powertrain output torque is present. Some conventional powertrain control systems employ a neutral idle control strategy. In this case, the transmission is automatically moved to neutral while idling to reduce fuel consumption and/or idle vibration. Vehicle rollback can occur in the time between brake pedal release and shifting of the transmission back into gear to propel the vehicle.
Current anti-rollback systems require the implementation of additional components and/or complex control strategies. As a result, vehicle manufacture is more complex and costly than desired.